1. Field of the Invention
Embodiments of the present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device having an adjustable viewing angle and a method of driving the LCD device. Embodiments of the present invention are suitable for a wide scope of applications. In particular, an embodiment of the present invention is suitable for providing an adjustable viewing angle for a sub-pixel region of an LCD.
2. Discussion of the Related Art
In general, a liquid crystal display (LCD) device relies on an optical anisotropy and a polarizability of liquid crystal molecules to produce an image. The optical anisotropy of liquid crystal molecules causes a refraction of light incident onto the liquid crystal molecules in accordance with an alignment direction of the liquid crystal molecules. Liquid crystal molecules are aligned in specific directions due to their long, thin shape. The alignment direction of the liquid crystal molecules can be controlled by applying an electric field thereto. Among LCD devices, active matrix liquid crystal display (AMLCD) devices have thin film transistors (TFTs) and pixel electrodes connected to the TFTs in a matrix arrangement. AMLCD devices have been widely used because of their high resolution and superiority in displaying moving images.
A twisted nematic (TN) mode LCD device includes a first substrate having a pixel electrode, a second substrate having a color filter layer and a common electrode, and a liquid crystal layer interposed between the first and second substrates. Liquid crystal molecules in the liquid crystal layer are driven by a vertical electric field generated between the pixel electrode and the common electrode. Accordingly, the TN mode LCD device has high transmittance and wide aperture ratio. However, the TN mode LCD device has a relatively narrow viewing angle. An in-plane switching (IPS) mode LCD device has been suggested to overcome the problem of the narrow viewing angle suffered by the TN mode LCD device.
FIG. 1 is a cross-sectional view of an IPS mode LCD device according to the related art. As shown in FIG. 1, an IPS mode LCD device includes a first substrate 110, a second substrate 120 and a liquid crystal layer 130 between the first and second substrates 110 and 120. A pixel electrode 112 and a common electrode 114 are formed on the first substrates 110. A voltage difference is applied between the pixel electrode 112 and the common electrode 114 to align the liquid crystal molecules in the liquid crystal layer 130. The aligned liquid crystal molecules are arranged along a horizontal electric field 100 generated between the pixel electrode 112 and the common electrode 114. The viewing angle increases because the variation in refractive index with respect to the viewing angle is relatively small.
FIG. 2 is a schematic plane view of an array substrate for an IPS mode LCD device according to the related art. Referring to FIG. 2, a gate line GL and a data line DL are formed on a substrate. The gate line GL crosses the data line DL to define a sub-pixel region “SP.” A common line “Vcom” is formed to be parallel to and spaced apart from the gate line “GL.” A switching element, such as a thin film transistor (TFT) “T,” is connected to the gate line GL and the data line “DL.” A plurality of common electrodes 252 and a plurality of pixel electrodes 212 are formed in the sub-pixel region “SP.” The plurality of common electrodes 252 extend from the common line “Vcom” and are parallel to the data line “DL.” The plurality of pixel electrodes 212 extend from an extension line 220 connected to the TFT “T” and alternate with the plurality of common electrodes 252. Gap portions 290 between the pixel electrodes 212 and the common electrode 252 correspond to a substantial aperture region where liquid crystal molecules are driven by a horizontal electric field.
As shown in FIG. 2, the pixel electrode 212 and the common electrode 252 of the related art IPS mode LCD device have a straight bar shape. Such a shape of the pixel electrode 212 and the common electrode 252 produces a mono-domain structure causing shortcomings of the IPS mode LCD device, such as a gray level inversion. An IPS mode LCD device having zigzag-shaped electrodes has been suggested to surmount the shortcomings.
FIG. 3 is a schematic plane view of an array substrate having a zigzag shaped electrode for an IPS mode LCD device according to the related art. Referring to FIG. 3, a pixel electrode 212 and a common electrode 252 have a zigzag shape having at least one bent portion. Not shown in FIG. 3, the data line DL may have a zigzag shape corresponding to the pixel electrode 212 and the common electrode 252. When a voltage is applied to the pixel electrode 212 and the common electrode 252, liquid crystal molecules are re-aligned along at least two directions due to the zigzag shape of the pixel electrode 212 and the common electrode 252. Accordingly, the IPS mode LCD device may have a multi-domain structure. In the multi-domain structure, a color shift phenomenon is reduced and gray level inversion is improved. As a result, the IPS mode LCD device has a relatively wide viewing angle allowing many users to concurrently view the displayed images.
However, some applications require a narrow viewing angle for the displayed images to be viewable by a limited number of users, for example, a single user. For example, an LCD device may be used as a display in an internet banking environment and in an automatic teller machine. In such circumstances, it is desirable that the displayed images could only viewed by a customer standing within a restricted viewing angle of the display and not by people standing or passing by to protect the customer for eventual prying eyes. A side viewing angle of the LCD device can be adjusted using a filter. However, using a filter for adjusting the side viewing angle complicates the fabrication process for the LCD device, and increases power consumption and fabrication cost.